About a month after she and Johnny announced they had parted ways, everyone's scambling to figure out why.

Frankly, the only reason anyone can agree on (reportedly according to Vanessa) is his attraction to Rum Diary co-star Amber Heard.

'Vanessa's devastated that Johnny's dumped her," a source close to her told Now magazine (via The Daily Mail). "She blames Amber and calls her a man-stealing, two-bit nobody and has vowed to not let her anywhere near their children."